$Ab$ $initio$电子阻止本领和通道慢光离子在HfO $_{2}$中的阈值效应
$Ab$ $initio$ electronic stopping power and threshold effect of channeled slow light ions in HfO$_{2}$
摘要：
我们提出了$ab$ $initio$研究质子和氦离子在绝缘材料HfO $_{2}$中的电子阻止本领。计算是在沟道条件下，采用Escherfest动力学和实时，时间相关的密度泛函理论与不同的碰撞参量。与现有实验的比较表明，这种方法提供了一个准确的描述电子阻止本领。在低能区，对质子和氦离子的阻止本领与速度成正比，符合线性响应理论。由于宽带隙的存在，预期在低于激发的极低速区域中会出现阈值效应。对于质子，阈值速度是可观察的，而在氦离子的情况下，它不出现。这表明当氦离子穿过晶体时，除了电子-空穴对激发之外，还存在额外的能量损失通道。通过对运动射弹的电荷状态的分析，发现氦离子与宿主原子之间存在明显的电荷交换行为，氦离子的失阈效应是由电荷转移引起的，而电荷转移也是导致氦离子能量损失的原因之一。
英文摘要：
We present $ab$ $initio$ study of the electronic stopping power of protons and helium ions in an insulating material, HfO$_{2}$. The calculations are carried out in channeling conditions with different impact parameters by employing Ehrenfest dynamics and real--time, time--dependent density functional theory. The satisfactory comparison with available experiments demonstrates that this approach provides an accurate description of electronic stopping power. The velocity-proportional stopping power is predicted for protons and helium ions in the low energy region, which conforms the linear response theory. Due to the existence of wide band gap, a threshold effect in extremely low velocity regime below excitation is expected. For protons, the threshold velocity is observable, while it does not appear in helium ions case. This indicates the existence of extra energy loss channels beyond the electron--hole pair excitation when helium ions are moving through the crystal. To analyze it, we checked the charge state of the moving projectiles and an explicit charge exchange behavior between the ions and host atoms is found. The missing threshold effect for helium ions is attributed to the charge transfer, which also contributes to energy loss of the ion.
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